This project consists of three parts. In the first part a plan is proposed to develop a quantitative description of the ventricle as a pump under in vivo conditions, taking into account its time-varying nonlinear properties. This plan includes the development of a novel technique for the measurement of phasic ventricular volume. In the second part a wide range of animal experiments is proposed for the purpose of arriving at a definitive interpretation of the physical phenomena observed in arteries. The approach will be guided by the theory developed for this purpose during previous years of this grant. The goal of the third part is to analyse the interaction between the ventricle and the arteries. This analysis will permit the assessment of the validity of the description of the ventricular pump and of that of the arteries. In addition, it will throw light on the issue to what extent the ventricle-artery combination controls itself.